Centrifugal classifier



April 1962 1 w. c. LAPPLE 3,031,080

CENTRIFUGAL CLASSIFIER Filed Sept. 21, 1960 2 Sheets-Sheet 1 IN V EN TOR. M41725? C. ZAP/ 1E BY www M April 24, 1962 w. c. LAPPLE 3,031,080

CENTRIFUGALCLASSIFIER Filed Sept. 21, 1960 2 Sheets-$heet 2 INVENTOR. M AZTEIQ C. LAPPLE ATTOQNEY United States Patent 3,031,080 CENTRIFUGAL CLASSIFIER Walter C. Lapple, Mountainside, N.J., assignor to United States Steel Corporation, a corporation of New Jersey Filed Sept. 21, 1960, Ser. No. 57,479 6 Claims. (Cl. 209-144) This invention relates to an improved classifier for separating particulate material into size fractions and to an improved classifying method.

An object of the invention is to provide an improved classifier and classifying method which afford a rapid and accurate separation of a sample into size fractions with results readily duplicated.

A further object is to provide an improved classifier and classifying method in which adjustments readily are made to vary the size where separation is eifected.

A more specific object is to provide an improved classifier and classifying method which utilize both centrifugal and drag forces on each particle in a sample to effect a separation of the sample into size fractions.

In accomplishing these and other objects of the invention, I have provided improved details of structure, a preferred form of which is shown in the accompanying drawings, in which:

FIGURE 1 is a side elevational view, with parts broken away, of a classifier constructed in accordance with my invention;

FIGURE 2 is a 'vertical sectional view on a larger scale of the rotatable spindle and associated parts embodied in my classifier; and

FIGURE 3 is a diagrammatic vertical sectional view of my classifier and associated apparatus illustrating the air flow.

My classifier includes a frame 10, which supports an elongated upright chamber 12. The lower portion of the chamber contains a perforate horizontal partition 13. An inlet 14 leads to the space within the chamber beneath this partition and is connected to a suitable source of a high velocity fiuidizing gas, preferably compressed air. A removable cap 15 covers the upper end of the chamber and contains an inlet 16 open to the atmosphere. I introduce a sample M of particulate material to the chamber through the top for separation into two size fractions. I introduce gas to the bottom of the chamber and thus iluidize the sample. Patition 13 supports the resulting fluidized bed of particles. Air within chamber 12 remains under negative pressure to avoid dust losses. A mechanical vibrator 17, per se of conventional construction, on the outside of the chamber prevents particles from adhering to the chamber walls through electrostatic attraction.

Frame carries a pair of opposed bearings 18 located intermediate the height of chamber 12. A tubular spindle 19 is journaled in bearings 18 with its axis of rotation extending across the diameter of the chamber. I choose the size of sample so that the upper surface of the fluidized sample bed lies near the spindle. The frame also carries a motor 20 which drives the spindle through a belt and pulley connection 21. As best shown in FIG- URE 2, a rubber jacket 22 surrounds the central portion of the spindle to minimize impact grinding of particles which strike the outside of the spindle. The portions of the spindle and jacket walls within chamber 12 contain perforations 23 of a size somewhat larger than the size at which particles are separated. Particles from the bed within chamber 12 are drawn into the bore of the spindle, but its rotation produces centrifugal force which returns oversize particles to the bed. Some oversize particles of course may remain in the lower portion of the bed without reaching the spindle. Undersize particles are withdrawn from the end of the spindle, as hereinafter explained.

The bore of spindle 19 houses a fixed pressure distributing tube 24 which extends beyond the spindle and its bearing 18 at the left. Tube 24 contains perforations 25 of smaller size than perforations 23 in the spindle, but still larger than the separation size. As the spindle turns, tube 24 assures a uniform pressure drop across the perforations. The exterior of tube 24 carries a screw thread 26 to prevent particles which enter the space between the tube and spindle from becoming trapped. The hand of this thread and the direction of spindle rotation are such that a swirling current of air within the thread roots moves toward the right. The right or drive end of the spindle contains a constricted bore 27 through which a small amount of air is drawn to return such particles to the tube bore.

A pipe 28, which contains a pressure tap 29, is fixed to the left end of tube 24 and connects the tube bore with the inlet of a conventional cyclone 30 shown in FIGURE 3. Air drawn through tube 28 withdraws undersize particles and delivers them to the cyclone, which separates such particles from the air stream. Undersize particles from the sample thus collect at the bottom of the cyclone. Air discharges from the cyclone through a pipe 31 at the top. Pipe 31 leads to a conventional filter 32 and thence to a suitable vacuum source indicated by legend in FIGURE 3. The filter collects any undersize particles which escape the cyclone. I operate the classifier long enough to remove all undersize particles from the sample. Oversize particles of course remain in the chamber 12, and can be dumped at the conclusion of the operation.

A flow control tube 33 is connected to pipe 31 via a pipe 34. Tube 33 tapers downwardly and contains a weighted ball-type valve 35, preferably of rubber. The purpose of tube 33 is to maintain a constant and predetermined flow of air through spindle 19. The magnitude of negative pressure at the pressure tap 29 furnishes an indication of the rate of air flow through the spindle. As classification of a sample progresses, the filter becomes partially clogged and offers increasing resistance to passage of air. Since the vacuum is constant, air flow through the filter diminishes, but flow through the spindle is maintained constant by diminishing the flow through tube 33. The ball-type valve 35 automatically cuts off this flow as needed.

The size at which particles are separated from one another is a function of the volume rate of the air and the rotational speed imparted to the particles, provided the air temperature, the particle density, and the physical dimensions of the classifier are maintained constant. Thus I can readily calibrate any classifier constructed in accordance with my invention as to the necessary air flow and speed to separate particles at difierent sizes at any temperature and density. I can of course readily vary the separation size by changing the air flow and/or speed.

While I have shown and described only a single preferred embodiment of my invention, it is apparent that modifications may arise. Therefore, -I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A classifier for separating particulate material into size fraction comprising a chamber adapted to receive a sample of the material, means for introducing a fluidizing gas to the lower end of said chamber and thus fiuidizing the sample therein, said chamber having an air inlet at its upper end, a perforate tubular device journaled in said chamber and adapted to receive particles from the fluidized sample, drive means for rotating said device and thus returning oversize particles to the chamber by centrifugal force, and vacuum means connected to said device for drawing air into said chamber via said inlet and withdrawing undersize particles from said device.

2. A classifier for separating particulate material into size fractions comprising an elongated upright chamber adapted to receive a sample of the material, means for introducing a fluidizing gas to the lower end of said chamber and thus fluidizing the sample therein, said chamber having an air inlet at its upper end, a perforate spindle journaled on a horizontal axis across said chamber and having a bore adapted to receive particles from the fluidized sample, drive means for rotating said spindle and thus returning oversize particles to the chamber by centrifugal force, vacuum means connected to one end of the bore of said spindle for drawing air into said chamber via said inlet and withdrawing undersize particles from said bore, and means for collecting undersize particles thus withdrawn.

3. A classifier for separating particulate material into size fractions comprising an elongated upright chamber adapted to receive a sample of the material, means for introducing a fluidizing gas to the lower end of said chamber and thus fiuidizing the sample therein, a tubular spindle journaled on a horizontal axis across said chamber and containing perforations through its walls, a pressure distributing tube fixed within said spindle and containing perforations through its walls smaller than said first named perforations, said tube having a bore adapted to receive particles from the fluidized sample transmitted through the perforations in said spindle and tube, drive means for rotating said spindle and thus returning oversize particles to the chamber by centrifugal force, vacuum means connected to one end of said tube bore for withdrawing undersize particles therefrom, and means for collecting undersize particles thus withdrawn.

4. A classifier as defined in claim 3 in which said tube has external screw threads for carrying particles trapped between the tube and spindle to the end of the tube opposite the connection to said vacuum means, and said spindle has a constricted bore in its end for admitting air to return such particles to the tube bore.

5. A classifier as defined in claim 3 comprising also a perforated rubber jacket surrounding said spindle to minimize impact grinding of particles which strike the spindle.

6. A classifier as defined in claim 3 in which the means for collecting undersize particles'includes a cyclone and a filter interposed between said tube bore and said vacuum means, said cyclone having an inlet connected to said tube bore and a discharge to which said filter is operatively connected, said vacuum means being operatively connected to said filter, said classifier also including means operatively connected to said filter for maintaining a constant flow of'air through said spindle asthe resistance of said filter to passage of air increases by reason of partial clogging with undersize particles.

References Cited in the file of this patent UNITED STATES PATENTS 2,087,645 Hermann July 20, 1937 2,361,758 De Fligue Oct. 31, 1944 2,939,579 Hardinge June 7, 1960 OTHER REFERENCES Perry: Chemical Engineers Handbook, 1950, pages 1032, 1033, McGraw-Hill Book Company, New York. 

